Chapter 18: The Representative Elements

The compound $N{F}_3$ is quite stable, but ${\text{NCl}}_3$ is very unstable ${\text{NCl}}_3$ was first synthesized in 1811 by P. L. Dulong, who lost three fingers and an eye studying its properties). The compounds ${\text{NBr}}_3$ and ${\text{NI}}_3$ are unknown, although the explosive ${\text{NI}}_3$. $N{H}_3$is known. How do you account for the instability of these halides of nitrogen?

Lewis structures can be used to understand why some molecules react in certain ways. Write the Lewis structure for the reactants and products in the following reactions.

a. Nitrogen dioxide dimerizes to produce dinitrogen tetroxide.

b. Boron trifluoride accepts a pair of electrons from ammonia, forming_{${\mathbf{\text{BF}}}_{\mathbf{3}}{\mathbf{\text{NH}}}_{\mathbf{3}}$}.Give a possible explanation for why these two reactions occur.

Use bond energies (Table) to show that the preferred products for the decomposition of_{${\mathbf{\text{N}}}_{\mathbf{2}}{\mathbf{\text{O}}}_{\mathbf{3}}$}are${\mathbf{\text{NO}}}_{\mathbf{2}}$and_{$\mathit{N}\mathit{O}$}rather than${\mathit{O}}_{\mathbf{2}}$and_{${\mathbf{\text{N}}}_{\mathbf{2}}\mathbf{\text{O}}$}. (The_{$\mathbf{N}\mathbf{-}\mathbf{O}$}single bond energy is$\mathbf{201}\mathbf{}\mathit{k}\mathit{J}\mathbf{/}\mathit{m}\mathit{o}\mathit{l}$.) (Hint: Consider the reaction kinetics.)

Ammonia is produced by the Haber process, in which nitrogen and hydrogen are reacted directly using an iron mesh impregnated with oxides as a catalyst. For the reaction ${\mathbf{\text{N}}}_{\mathbf{2}}\mathbf{\left(}\mathit{g}\mathbf{\right)}\mathbf{+}\mathbf{3}{\mathbf{\text{H}}}_{\mathbf{2}}\mathbf{\left(}\mathit{g}\mathbf{\right)}\mathbf{\rightleftharpoons }\mathbf{2}{\mathbf{\text{NH}}}_{\mathbf{3}}\mathbf{\left(}\mathit{g}\mathbf{\right)}$

equilibrium constants ( ${\mathit{K}}_{\mathbf{s}\mathbf{p}}$values) as a function of temperature are

_{$$\begin{gathered} {\mathbf{300}}^{\mathbf{°}}\mathit{C}\mathbf{,}\mathbf{}\mathbf{4}\mathbf{.}\mathbf{34}\mathbf{\times }{\mathbf{10}}^{\mathbf{-}\mathbf{3}} \\ {\mathbf{500}}^{\mathbf{°}}\mathit{C}\mathbf{,}\mathbf{}\mathbf{1}\mathbf{.}\mathbf{45}\mathbf{\times }{\mathbf{10}}^{\mathbf{-}\mathbf{5}} \\ {\mathbf{600}}^{\mathbf{°}}\mathit{C}\mathbf{,}\mathbf{}\mathbf{2}\mathbf{.}\mathbf{5}\mathbf{\times }{\mathbf{10}}^{\mathbf{-}\mathbf{6}} \end{gathered}$$}

Is the reaction exothermic or endothermic?

List two major industrial uses of hydrogen.

The synthesis of ammonia gas from nitrogen gas and hydrogen gas represents a classic case in which a knowledge of kinetics and equilibrium was used to make a desired chemical reaction economically feasible. Explain how each of the following conditions helps to maximize the yield of ammonia.

a. running the reaction at an elevated temperature

b. removing the ammonia from the reaction mixture as it forms

c. using a catalyst

d. running the reaction at high pressure

Write an equation for the reaction of hydrazine with fluorine gas to produce nitrogen gas and hydrogen fluoride gas. Estimatefor this reaction, using bond energies from Table$\mathbf{\text{13.6}}$.

In each of the following pairs of substances, one is stable and known, whereas the other is unstable. For each pair, choose the stable substance, and explain why the other compound is unstable.

a. ${\mathbf{\text{NF}}}_{\mathbf{\text{5}}}$or${\mathbf{\text{PF}}}_{\mathbf{\text{5}}}$

b.${\mathbf{\text{AsF}}}_{\mathbf{\text{5}}}$or${\mathbf{\text{AsI}}}_{\mathbf{\text{5}}}$

c.${\mathbf{\text{NF}}}_{\mathbf{3}}$or${\mathbf{\text{NBr}}}_{\mathbf{\text{3}}}$

Write balanced equations for the reactions described in Table $\mathbf{\text{18.13}}$for the production of $\mathbf{\text{Bi}}$and $\mathit{S}\mathit{b}$.

Phosphoric acid$\left({\text{H}}_{\text{3}}{\text{PO}}_{\text{4}}\right)$is a triprotic acid, phosphorous acid$\left({\text{H}}_{\text{3}}{\text{PO}}_3\right)$is a diprotic acid, and hypo phosphorous acid$\mathbf{\left(}{\mathbf{\text{H}}}_{\mathbf{\text{3}}}{\mathbf{\text{PO}}}_{\mathbf{2}}\mathbf{\right)}$is a monoprotic acid. Explain this phenomenon.